Page 133 - Medicinal Plants_PharmD general

Properties of calcium oxalate:

Calcium oxalate crystals are insoluble in water, glycerin, alcohol,

phenolic mountants such as phenol and cresol and in oil of cloves. They

are not immediately affected by solution of caustic alkalies or of chloral

hydrate; being at first apparently unaffected but, in the course of time

especially when present in a small quantity, or on warming, the crystals are

gradually attacked, destroyed and finally dissolved.

Calcium oxalate is differentiated from other crystalline substances

e.g. calcium carbonate, calcium tartarate, etc., which may be present in the

plant but of less frequent occurrence, by the following:

1) Calcium oxalate is insoluble in acetic acid but dissolves in hydrochloric

acid without effervescence (c.f. calcium carbonate).

Calcium oxalate + HCI calcium chloride + oxalic acid

2) It is decomposed when in contact with sulphuric acid (20% or more)

without effervescence. Calcium oxalate crystals, disappear and new

needle-shaped crystals of calcium sulphate often forming radiating

groups, slowly make their appearance in the vicinity of the original

crystals.

H COO HCOOH

Ca + H2SO4 CaSO4 +

H COO HCOOH

3) It is only very slowly affected by solution of caustic alkalies: the

crystals disappear after a few weeks; being replaced by crystals of a

different form, probably consisting of calcium, sodium or potassium

carbonate (c.f. calcium tartrate which dissolves very rapidly).

Forms of Crystals:
The crystals of calcium oxalate occur in drugs in different forms.

Nevertheless, the form or forms found in a particular plant are practically
constant and, therefore, often afford a valuable aid in the identification of

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